Conventional machining and other stock removal techniques such as turning, milling and planing involves the shaping of a desired article from a blank by the removal of stock by either moving the workpiece relative to a stationary tool, or by moving the tool relative to stationary workpiece or combinations thereof. In turning for example, one end of a workpiece is gripped in the chuck of a lathe with the other end engaged and centered by the tail stock. The work is rotated with regard to a cutting tool which may be translated in a direction parallel to the axis of rotation as well as moved inwardly toward the axis of rotation. By gradually advancing the tool toward the workpiece, chips are removed until the workpiece obtains its desired configuration. The result is that 100% of the stock that has been removed, has been cut and becomes waste in the form of chips, slivers and the like.
Likewise, in the conventional milling process, a workpiece is placed on a table in a position to be engaged by a rotating milling cutter. The work table translates the workpiece relative to the cutter and simultaneously the cutter may be moved toward the workpiece increasing the depth of cut until the desired shape is obtained. Again the result is that all of the stock removed to obtain the desired shape of the workpiece becomes waste, and energy is dissipated over 100% of the removed stock. The same is true of shaping and planing. These techniques have been used for decades in woodworking, metalworking, stone cutting etc.
Not all techniques however require the cutting or stock removing energy to be dissipated over the entire volume of material removed, as for example the simply technique of sawing. A cut is made by a blade, which for the most part removes a solid piece of the stock, with the only energy being dissipated in the volume which forms the kerf. Thus, from an efficiency standpoint, the cutting energy is dissipated over a volume less than the entire volume of material removed.
Many exotic materials having high strength and hardness have been developed for and as a result of the space age. While they are extremely useful in the environments for which they were developed, they are for the most part difficult to machine when employing conventional cutting techniques which rely upon the mechanical removal of the material described above.
Such material would include for example, aluminum oxide, zerconium oxide, steel of 60 Rockwell and harder, composite materials, as for example, epoxy with fillers such as carbon or glass fibers. These materials because of their hardness or brittleness or high tensile strength offer considerable resistance to conventional machining processes which depend upon the complete mechanical removal of volume of material to produce a final desired shape.
Concurrently with the evolution of space age materials has been the development of laser beam technology and in the area of material removal technique has been primarily involved in micromachining such as surface engraving, the drilling of small holes in hard materials, scribing in the electronic industry, and the cutting of sheet material.
Precise and accurate stock removal can be obtained by melting or vaporizing portions of a workpiece to obtain the desired shape by directing concentrations of light energy to the workpiece which may be either stationary or moving. For example the use of a laser in conjunction with a punch press is disclosed in U.S. Pat. No. 4,201,905. A workpiece, such as sheet of metal on a worktable is moved by grippers beneath a fixed laser, which is positioned to project a beam downwardly on a vertical axis. Pieces are cut from the workpiece by melting holes on a continuous line. This technique is generally limited to work on relatively thin sheets of stock.
Single lasers have been used in conjunction with metal turning. For example, U.S. Pat. No. 3,404,254 to Jones discloses a machine and technique for engraving the surface of a circular body by laser melting. A single laser beam is directed to the surface by a rotating cylinder. As the cylinder rotates the laser is translated axially of the cylinder to melt a continuous line in its surface. The cylinder is then rotated at sufficient speed to remove the melted localized portions from the cylinder by centrifugal force. While the desired results are achieved by engraving, the entire volume of stock removed is subjected to the laser energy.
In like manner, U.S. Pat. No. 4,170,726 to Okuda discloses directing a laser beam at selected portions of the surface of the workpiece tangentially of the path of rotation. Thereafter the molten material is removed by means of shaping mechanically of the workpiece. Hence, all of the stock removed is subject not only to the laser energy but the energy imparted by the shaper.
Similarly U.S. Pat. No. 3,499,136 to Nunnokhoven et al. describes a rotating body being balanced by removing the material from the body while it is rotating. The stock is removed by a laser which melts small particles of material from the rotating workpiece. This too requires all of the stock removed to be subjected to energy.
An object of the present invention is to utilize laser cutting techniques to shape a workpiece from materials which are not readily adaptable to normal metal cutting techniques and at the same time operating with a minimal expenditure of energy.
Another object of the invention is to remove stock from a workpiece to obtain a desired configuration without subjecting all of the removed stock to energy dissipation.
Still another object of the present invention is to remove stock from a workpiece without the creation of undue waste and whereby portions of the workpiece which are removed may be functionally utilized rather than being turned into discardable waste.